Reporter: It was the biggest kidnapping since the lindberg baby -- paul fronczak, stolen at birth by a fake nurse. His angelic face peering from the front page was the last anyone had seen of him. Left behind were an empty crib and two broken hearts. A year passed. And then, one day, their phone rang. 800 miles away in newark, new jersey, a boy had been found. The fbi contacted my parents and said, "we think we found your, your son." So my parents had to drive to new jersey. Reporter: And they said this is our baby? This is paul. Reporter: We recognize him? Yes. Reporter: Whoever abandoned the boy had dressed him up, wheeled him to a department store in a new stroller, and walked away. You have someone who places a child in a place that's going to be found and found quickly. So it's not somebody that wants this child to -- to die or be harmed in any way. Reporter: This is a picture of you when you were found in newark after you were abandoned. So, how do you feel when you see yourself? That's my first baby picture, that's all I have so far. That's it. Reporter: This is the boy new jersey authorities called "unknown male number one" in the arms of a nurse from a newark hospital. Somebody wheels a stroller, puts you here, walks away. And never looks back. Reporter: And never looks back. It's -- it's crazy. Reporter: Last week, we returned to newark, new jersey with paul fronczak, back to the very place where someone left him sitting in a stroller 48 years before. Is it emotional for you to be here? It is. It's -- I feel eerie. I feel anxious. I feel excited. I feel sad. All those things. Reporter: Paul fronczak back on a new jersey street, a crossroad in his life. I wish these walls could talk, you know, maybe we could learn somethin'. I don't know, it's -- it just -- I -- I -- I can't believe that this actually happened, and i can't believe it's my life. Reporter: In the summer of 1966, the fronczaks believed their family miraculously had been reunited. The fbi had ordered a series of blood tests on the abandoned boy. And compared photographs of his left ear with that of the fronczak baby. Eventually confident enough that they informed the fronczacks, who said they had no doubt the child was theirs. They brought him home to chicago and, for the second time, named him paul joseph fronczak. Your parents were convinced. Why were they so convinced? I feel it's the fbi, the fbi is like the, the epitome of authority, and when they say this is your child, I would believe them. That's it. Reporter: And that ended the search. Yes. Reporter: At that point. Everyone stopped looking for paul fronczak, that was the end of the story? Yes. Reporter: Tell me about your childhood. Was it happy? Yeah, it was a great childhood. Barbecues, family get-togethers, family vacations. Reporter: The family so often filmed in heartbreak, now recorded home movies of their own. The star of every celebration of course, was paul. They had missed his first step, first word, first birthday. But paul was now back where he belonged. Blissfully unaware of his past until years later when you were 10 years old, you had a shocking discovery, tell me about it. I was looking for christmas presents, and snooping around the house, and I found all these boxes. And it turned out it was a box of clippings and a bunch of cards and letters all about a kidnapping. Reporter: Did you ask your parents about it? I did. I asked them, you know, "what is this?" And they said, "well, you were kidnapped, we found you." Reporter: Just like that, you were kidnapped, we found you? And that's all that matters, you're our son, we love you. Reporter: How did your parents explain what happened to you? They really didn't talk about it, it was something that we really didn't bring up in the house. It was a very touchy subject. Reporter: Did you ever feel that there was anything out of the ordinary when you were growing up? Well i, I did notice that i didn't resemble anybody in my family. Reporter: You had a brother? Correct. Reporter: And he looked like your parents? Exactly like my dad. 100%. Reporter: And you didn't at all? Not at all. Reporter: When he grew up, paul pursued a career as an actor. His resemblance to george clooney got him work as a stand-in in "ocean's eleven" movies. Today, paul works for a college in nevada where he lives with his wife, michelle and their daughter, emma. You remember how you felt when paul said, "i'm not really sure who I am?" The first time he told me i thought he was joking. I thought he was just kidding around. But then, once I realized it was true and I saw the newspaper clippings I felt - - very sad for his parents and sad for him. Reporter: How do you think it has shaped him? I think as a 10-year-old boy, when he first saw those newspaper clippings, not realizing who he was, I'm sure that that has somehow shaped him and that's done something to him over the years. It's just sad. Reporter: Was it sort of there in the back of your mind, this peculiar thing? It was really a big part of me through my whole life, and it's just gotten bigger and bigger and bigger. Reporter: Who am i? Who am i? Yeah. Reporter: Then, last year paul happened to see a dna test kit for sale at a local drug store. At last, an easy answer to the question that had followed him all his life. The hard part -- asking his parents for a dna sample, forcing them to travel back in time, to the most painful part of their lives. It's something I wanted to do for a long time, but I never really had the nerve to, to ask my parents.

This transcript has been automatically generated and may not be 100% accurate.

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